According to Bloomberg, Apple in on track to break its own iPad sales record, as the company is expected to sell a whopping 600,000 iPad 2s over the weekend. In comparison, Apple sold 300,000 original iPads when it launched back in April 2010, in less than 24 hours. Even if not officially launched yet, the tablet already proved to be extremely popular. For instance, the Apple online store started to accept orders at 1 AM Pacific Time this morning, and while iPad 2s initially showed shipping lead times of about 3 days, less than 5 hours later, the store apparently ran out, as all models now appear to be backlogged for at least 2 weeks. Meanwhile, Mike Abramsky from RBC Capital Markets is expecting the iPad 2 to fare extremely well this year, with up to 28 million units sold before December 2011. While the vast majority of iPad 2 owners will be new buyers, 20-percent of first generation iPad owners are expected to upgrade to the iPad 2 within less than a year. The iPad 2 will be available at 5PM today (local time), at all of the 236 Apple retail stores, as well as most Best Buy, Target, Walmart, at&t and Verizon stores. International buyers will need to wait a couple of extra weeks, as the device will not be released in other countries before March 25. Alternatively, international buyers will be happy to know that hundreds of iPad 2s are already available for pre-order on the gray market, or via eBay. Note that there is no guarantee the seller will actually be able to purchase the iPad 2 on your behalf today, and be prepared to pay a hefty premium for the device.